Interpretive Summary: Expressed DNA sequences were taken from 47 cDNA libraries and were physically mapped to specific chromosome regions of wheat homoeologous group 5 chromosomes. We found that the expressed sequences were not scattered from one end to the other of the group 5 chromosomes, but seemed to be clustered in more distal regions of the chromosomes. This information will be of value to wheat geneticists in physical mapping genes or gene complexes and in map-based cloning of genes located on wheat group 5 chromosomes.

Technical Abstract:
The objective of this study was to establish a high-density chromosome bin map of homoeologous group 5 (5A, 5B, 5D) of wheat to study gene distribution and to perform comparative studies with rice. A total of 2555 loci, including 2338 loci mapped with 1052 EST probes and 217 previously mapped markers were used to construct a consensus deletion bin map of group 5. A relatively higher number of ESTs were mapped on chromosome 5B (38%) compared to 5A (34%) and 5D (28%). Differences in the level of polymorphism among the three chromosomes were partially responsible for these differences. A higher level of duplicated loci was found on chromosome 5B (42%). Three times more ESTs were mapped on the long arms than on the short arms, and for both arms, a significantly higher number of ESTs, loci, and duplicated loci were mapped on the distal halves than on the proximal halves of the chromosomes. Good overall co-linearity was observed among the three homoeologous group 5 chromosomes, except for the previously known 5AL/4AL translocation and a putative small pericentric inversion in chromosome 5A. Statistically significant co-linearity was observed between low copy number ESTs from wheat homoeologous group 5 and rice chromosomes 12 (88 ESTs), 9 (72 ESTs), and 3 (84 ESTs). This co-linearity was used to infer the order of ESTs within the chromosome bins.